Stabilized organo-boron fuels



United States Patent 3,130,019 STABILIZED ORGANO-BORON FUELS Edward M. Butler, Dover, and Marvin M. Fein, Westfield, N.J., assignors, by mesne assignments, to Thiokol Chemical Corporation, a corporation of Delaware No Drawing. Filed Nov. 27, 1957, Ser. No. 699,425 8 Claims. (Cl. 44-76) This invention relates to high energy organo-boron fuel compositions having an increased spontaneous ignition temperature.

The use of high energy organo-boron fuels is described in application Serial No. 540,142, now Patent No. 3,052,- 725, filed October 12, 1955, of Altwicker et a1.

Fire hazards associated with the use, storage and shipment of high energy fuels used in ram-jets, rockets and the like presents a serious problem. Spillage of high en ergy fuel onto a hot surface presents a definite hazard insofar as fire and explosion are concerned. For example, the leakage or spillageof high energy boron fuels onto a hot engine part during engine operation or flight of an aircraft can cause a dangerous fire or explosion resulting in the complete destruction of the aircraft. The spillage during storage or shipment of such a boron fuel likewise can result in equally disastrous consequences.

It has been found that the spontaneous ignition temperature (the minimum temperature at which the fuel and. air will ignite without .the assistance of a flame or spark) of organo-borane high energy fuels such as the lower alkyl pentaboranes and the lower alkyl decaboranes can be raised materially by the addition of small quantities of iodine or certain iodine containing compounds which are soluble in the fuel such as carbon tetraiodide and iodoform.

Suitable lower alkyl pentaboranes are those in which the alkyl groups contain from 1 to 5 carbon atoms and which can be prepared, for example, according to the method described in application Serial No. 540,142, filed October 12, 1955, of Altwicker et al., now Patent No. 3,052,- 725. Suitable lower alkyl decaboranes are those in which the alkyl groups contain from 1 to 5 carbon atoms and which can be prepared, for example, according to the method described in application Serial No. 540,141, filed October 12, 1955, of Altwicker et al., now Patent No. 3,109,030.

The amount of the additive in the fuel compositions of the invention can be varied widely but is generally within the range from about 0.3 to 5% by Weight of the fuel composition. Less than about 0.3% appears to produce no substantial increase in spontaneous ignition temperature and more than about 5% detracts from the high energy value of the fuel.

The following examples illustrate in detail embodiments of this invention, but are not to be considered limiting.

Example 1 This experiment is conducted with a modified Setchkin apparatus, consisting of a one liter reaction flask positioned in a silicone oil bath. The reaction flask is situated in the oil bath with only the neck of the flask protruding and is kept in position by means of a weighted seat attached to the flask by a series of wire straps. The temperature of the oil bath is accurately controlled to plus or minus 0.5 C. with a Micro-set thermoregulator connected to an electronic relay. Heat is supplied to the bath by means of two 400-watt quartz heating elements and the temperature is kept uniform by the use of a high speed stirrer. The bath is insulated with asbestos and fitted with a Masonite cover through which the neck of the flask extends. The temperature of the oil bath and of the interior of the flask are measured by means of 3,130,019 Patented Apr. 21, 1964 glass-sleeved thermocouples (with bare tips) and a Leeds Northrup potentiometer. The flask is fitted with a twohole stopper; one passage for the thermocouple and the other for the ejection of the charge. The reliability of this apparatus was checked by measuring the spontaneous ignition temperature of carbon disulfide and ethylether both in this apparatus and the conventional Setchkin apparatus. The values were in excellent agreement within about two degrees C.

The procedure followed in establishing the spontaneous ignition temperature of various organo-borane fuels and fuel-additive blends consisted of a series of experiments at difierent temperatures using a 0.2 ml. test sample. In conducting an experiment the temperature of the oil bath was adjusted to -0.5 C. of the desired test temperature. Suificient time was allowed to permit thermal equilibrium to be attained between the air in the flask and the oil bath. When the temperatures inside of the flask and in the oil bath were equal (i0.5 C.), the glass-sleeved thermocouple was removed from the flask and a charge of 0.2 ml. of the fuel was rapidly injected into the flask by means of a hypodermic syringe fitted with a 10-inch No. 22 gauge needle. The needle was bent so that 'the operators hands would not be over the neck of the flask while injecting the charge. This injection provided the dispersion necessary for rapid evaporation and nearly simultaneous initiation of the reaction throughout the flask. The reaction was permitted to proceed without any alteration of temperature.

The experiments were repeated at higher temperatures until ignition occurred within two minutes after injection of the charge. The 2-minute interval, after the injection of the charge, was the criterion used for determining the spontaneous ignition temperature. Generally, ignition of the organo-borane fuels was indicated by an extremely loud report. Although the sound was quite intense, in no case did the flask break. After each test, the flask was purged by a jet of air in order to reduce the amount of oxides or soot deposited on the walls. The flask was changed at regular intervals (after every 3 or 4 runs) during the preliminary tests for approximate determinations of the spontaneous ignition temperature and before each test in the final determinations.

The following values were obtained for the indicated boron fuels tested:

Fuel analysis:

Example 11 A cylindrical aluminum block 3" high and 7" diameter, containing 18 spherical holes in the surface each in diameter and 7 deep is placed upon a hot plate whose temperature could be controlled by means of a variable transformer. Two Chromel-Alumel thermocouples are placed in the side of this aluminum block; one thermocouple is near the surface and the second 1 /2" below the surface of the block.

In conducting a typical hot surface spontaneous ignition temperature measurement, the surface temperature is first accurately measured by means of the thermocouple imbedded just below the surface of the aluminum block. After the temperature has been recorded, 0.1 cc. of test liquid is dropped from a glass syringe through a 2-inch 22 gauge needle mounted 2" above the surface of the aluminum block. The liquid is dropped with care so that it will fall into one of the holes in the surface of the block. Ignition occurs (if at) within a few seconds after the liquid touches the hot surface. The following results were obtained:

Fuel analysis:

Decaborane percent 4 Monoethyldecaborane -do 61 Diethyldecaborane do 29 Triethyldecaborane do 6 Spontaneous ignition temperatures Iodine concentration (percent by weight) (degrees C.)

Iodoform concentration: 4.1 211 Fuel analysis:

Pentaborane(9) percent 0.44 Monopropylpentaborane(9) do 99.30 Dipropylpentaborane(9) do 0.25 Spontaneous ignition temperatures Iodine concentration (percent by weight) (degrees C.)

We claim:

1. A liquid high energy fuel composition comprising a material selected from the class consisting of lower alkyl pentaborane(9) and lower alkyl decaborane having incorporated therein an additive selected from the class consisting of iodine, carbon tetraiodide and iodoform in an amount sufficient to increase the spontaneous ignition temperature of the fuel composition in air.

2. A liquid high energy fuel composition comprising a material selected from the class consisting of lower alkyl pentaborane(9) and lower alkyl decaborane having incorporated therein an additive selected from the class consisting of iodine, carbon tetraiodide and iodoform in an amount from about 0.1 to 5.0% by weight of the fuel composition.

3. The composition of claim 2 in which the material is ethyl decaborane.

4. The composition of claim 3 in which the additive is iodine.

5. The composition of claim 3 in which the additive is carbon tetraiodide.

6. The composition of claim 3 in which the additive is iodoform.

7. The composition of claim 2 in which the material is propylpentaborane.

8. The composition of claim 7 in which the additive is iodine.

References Cited in the file of this patent Carpenter: Ind. and Eng. Chem., vol. 49, No. 4, April 1957, pages 42A-48A.

C. & En., May 27, 1957, pages 18-23. 

1. A LIQUID HIGH ENERGY FUEL COMPOSITION COMPRISING A MATERIAL SELECTED FROM THE CLASS CONSISTING OF LOWER ALKYL PENTABORANE (9) AND LOWER ALKYL DECABORANE HAVING INCORPORATED THEREIN AN ADDITIVE SELECTED FROM THE CLASS CONSISTING OF IODINE, CARBON TETRAIODIDE AND IODOFORM IN AN AMOUNT SUFFICIENT TO INCREASE THE SPONTANEOUS IGNITION TEMPERATURE OF THE FUEL COMPOSITION IN AIR. 